1. Field of the Invention
The present invention is related to the field of maritime transportation, and more specifically to shipping cargo across oceans using combinations of ships.
2. Description of the Related Art
The basic cargo freighter ship is the primary tool for transporting large amounts of goods across oceans. It is characterized by a monohull design and highly efficient diesel propulsion.
The economics of cargo transportation across oceans suggest increasing the size of the monohull design. That is because there are logistical efficiencies in shipping a large cargo at once, even though that makes the ship more expensive. Accordingly, the size of the cargo bays has been increasing, which in turn has presented technical problems.
A larger hull, as compared to a smaller hull, is subjected to disproportionate structural punishment by the waves encountered in the ocean. This is because of the inevitable larger length, and the frequent larger height of the larger hull.
The hull stresses are now described with reference to FIGS. 1-5. Referring to FIG. 1, a ship 50 rides at the top of a wave 52. The hull is subjected to vertical forces 54 and horizontal forces 56. The forces deform the hull towards assuming shape 58. The deformation is also known as xe2x80x9choggingxe2x80x9d.
Referring to FIG. 2, ship 50 rides at a bottom of a wave 62. The hull is subjected to vertical forces 64 and horizontal forces 66. The forces deform the hull towards assuming shape 68. The deformation is also known as xe2x80x9csaggingxe2x80x9d.
Referring to FIG. 3, ship 50 rides in a changing wave 72. The hull front and rear portions of the hull are subjected to opposite torsional forces 74, 76. The forces tend to deform the hull in a twisting motion.
Referring to FIG. 4, ship 50 is in the loading process in the calm water line 80 of a port. Two loads 82, 84, press the hull unevenly, causing downward vertical forces 86. The water counteracts them by causing upward vertical forces 88. The vertical forces apply shear to the hull, and deform it accordingly.
It will be appreciated that these forces are disproportionately large when the ship length is large. In addition, another type of deformation is because of the large ship height.
Referring to FIG. 5, ship 50 is turning, while even in calm water 90. Its tall hull is subjected to a horizontal force 92. Accordingly, it is deformed towards assuming shape 94. The deformation is also known as xe2x80x9crackingxe2x80x9d.
These deformations cause fatigue to the hull plates, which reduces the service life of the overall vessel. The deformations are dealt with by strengthening crucial junctions and support members between the hull sections and plates. This strengthening elevates design costs, manufacturing costs and maintenance costs of these vessels.
Additionally, the large shipping capacity of a single ocean going ship has increased other costs to those who ship cargo. The larger capacity makes it more likely that more cargoes will be combined. Combining cargoes in order to fill a large capacity ship imposes delays in shipping of those cargoes which arrive early at the port dock, relative to those which arrive late. This increases shipping costs, both on actual cash terms, and consumes more of the life of the product.
A problem identified by the inventor is that there has always been a cost for local shipping. Local shipping is transporting goods from the place of their production to the transoceanic port of origin. This cost includes loading, shipping, unloading, and storing, until the large cargo ship is ready for loading. This is a built in cost, whether local shipping is done by railroad or by river. This cost has been unavoidable so far, and increases the expense of shipping.
A common ocean going freighter can not be used to alleviate the burden of local shipping. To do this, it would have to visit local ports. First, it would rarely be economical to do so, except perhaps between large ports. Second, it is often physically impossible to go into rivers. Even though a river may be wide enough, it is usually not deep enough for the large draft of the freighter. And even if deep enough, it may have a low bridge over it, which the ship""s superstructure would not clear.
The present invention overcomes these problems and limitations of the prior art.
Generally, the present invention provides an oceantrain. An oceantrain is a convoy of an ocean tug generally towing a series of specially made cargo ships also called module ships. In some instances the ocean tug simply controls the cargo ship remotely, without being physically coupled with them.
Each cargo ship is a medium tonnage, independently powered, independently controllable, freight carrying vessel with an oceanworthy hull. The hulls preferably have a standardized external design, which makes them modular. Inside, each has cargo space for either generic cargo, or for special cargo, such as refrigerated cargo or containers. Their engines need be no more powerful than is required for river navigation.
Being of medium tonnage, the special cargo ships have low draft, and thus can go up a river preferably using autonomous navigation. Each has a minimum pilot accommodation, which reduces the required overhead, and can clear a bridge. Having a short length and low draft, they are very maneuverable.
Reaching a port in the river, the special cargo ship can be loaded locally, and then exit the river and go to a port of origin of a transoceanic journey. While waiting for that journey to start, there is no need to unload, store, or reload the cargo. This eliminates a portion of costs that so far were always present.
A number of module ships gathered in a port of origin are then grouped into an oceantrain. They are connected with each other end to end, with special couplers for towing. The oceantrain is completed with a special ocean tug, which provides additional power for the ocean voyage. Further, the ocean tug controls each of the towed vessels by a remote control system. As such, once the oceantrain is assembled, the pilot of each cargo ship is no longer needed. They can use a catwalk suspended under the coupler to walk up to the tug, for disembarking before the ocean voyage starts.
While crossing the ocean, the tug tows the series of the cargo ships. In addition, the engine of each cargo ship is running, and is further controlled by the tug. Controlling the power, braking, and turning of each cargo ship makes the whole oceantrain move like one unit, and under the direction of a single captain.
During the voyage, controlling is by electrical wire, and preferably by radio signals that may go through satellite. Thus the cargo ships can be controlled even when disengaged from the towed convoy. For going through short locks or other situations, the oceantrain can be disengaged into sections. The sections can travel alongside each other, while still remotely controlled by the tug. They can be recoupled once clearing the situation.
Once the ocean voyage is completed, the ocean train can be disassembled at the port of destination. Each cargo ship can be individually piloted to its destination for unloading. Some of these destinations may be upstream a navigable river, that an ocean going cargo freighter might not be able to reach due to its large draft and higher overhead.
The oceantrain accomplishes transoceanic voyages with smaller hulls. The smaller size results in less deformation, and therefore less fatigue. As such, the module ships have a greater service life than those of ocean freighters. Stresses are absorbed in the couplers, which are economical to replace.
The modularity of the individual module ships permits assembling quickly an oceantrain with diverse types of cargoes. This results in shorter waiting times for each type of cargo, which improves the economics of shipping every type of cargo.
The ability to use the ocean going hull past the transoceanic port of destination, e.g. also for river transportation, will alleviate the bottleneck at the ocean ports, and thus will offer more options to shippers. Schedules will become more flexible, and transportation by river, sea and ocean a more attractive option. The economics of shipping will change, especially for shipping a refrigerated cargo, or a chemical cargo that needs special containment.
The invention includes numerous other features and advantages. They will become more readily apparent from the following detailed description of a preferred embodiment, which proceeds with reference to the drawings.